Geology of the Philippines
Sean was here The Philippine Archipelago is surrounded by few major plate tectonics such as Eurasian Plate, Pacific Plate, Indo-Australian Plate, and minor plate called Sunda Plate. PACIFIC PLATE The Pacific Plate is entirely composed of an oceanic lithosphere created between 150 and 0 Ma ago. It presently occupies almost a third of the total terrestrial surface, less than it did 200 Ma ago (Le Pichon and Huchon, 1984). This plate has undergone a major kinematic reorganization 43 Ma ago, involving a 50-degree clockwise rotation with respect to hot spots (Clague and Jarrard, 1973). This rotation from a NNW to a WNW trajectory is presently manifested in the change of orientation of the Hawaiian - Emperor Islands volcanic chain from a WNW-ESE direction to the south to a NNWSSE direction to the north. Another kinematic reorganization involving a 10-degree clockwise rotation 5 Ma ago is mentioned by Cox and Engebretson (1985) and Seno and Maruyama (1984). EURASIAN PLATE The Eurasian plate is situated at the western side of the Philippine Archipelago. Its eastern margin is composed of fragments that originated at the southern China continental margin (i.e'., Macclesfield Bank, the Reed Bank, Palawan, Cagayan Ridge, Zamboanga Peninsula, and part of the north arm of the Sulawesi') (Rangin & Pubellier, 1990; Hall, 2002). These fragments are separated by Cenozoic marginal basins namely the South China Sea, the Sulu Sea '''and the '''Celebes Sea '''basins (Holloway, 1982; Rangin et al., 1990, Pubellier et al., 2003) (Figure 2.1). Another basin, the '''proto-South China Sea '''that opened within the Eurasian margin in the ?Paleocene and the ?Eocene, has entirely disappeared at a fossil subduction zone southeast of Palawan (Rangin et al., 1990; Pubellier et al., 2003). Note: Proto-South China opened during the Late Cretaceous '''according to Pubellier et al. (2006) INDO-AUSTRALIAN PLATE The Indo-Australian Plate is composed of both continental and oceanic crusts. The continental crusts are presently represented by India and Australia, while the oceanic portion is represented by the Indian Ocean. The creation of the oceanic crust between India and Australia corresponds to the separation of the continental masses around 150 Ma ago. From 43 Ma ago, the mid-oceanic ridge separating the two continental blocks became inactive. Since then, a single Indo-Australian Plate is moving northwards. The interaction of these three major tectonic plates is governed by their nature (oceanic/continental) and their relative movements. The entirely oceanic Pacific Plate subducts under the other plates: under the Eurasian Plate along the Japan Trench, under the Philippine Sea Plate along the Bonin-MarianasYap Trench System, and under the Indo-Australian Plate east of New Zealand. The mixed continental and oceanic crusts of the Indo-Australian Plate are presently colliding with the Eurasian Plate (in the Himalayas) and with a complex zone of insular arcs which have been active since the Mesozoic (in New Guinea, for example). Its oceanic portion is presently subducting under the Eurasian Plate along the Java Trench. PHILIPPINE SEA PLATE = OCEAN BASI = The subduction zones are represented on the east by the west dipping Philippine Trench traversing the eastern seaboard of the Philippines from Mindanao up to a point in Luzon and the East Luzon Trough. East dipping subduction zones include the Manila Trench, Negros Trench and Cotabato Trench. The southern termination of the Manila Trench is characterized by the transformation of the subduction of the South China Sea Plate into an arc-continent collisional deformation within Mindoro Isla The continental block is represented by northern Palawan, southern Mindoro, Romblon Island Group and Buruanga Peninsula in Panay Island, known collectively as the North Palawan Block. The Mindoro block consists of a pre-Upper Cretaceous low-grade metamorphic basement, overlain by Upper Cretaceous and upper Eocene strata. The Mindoro block records several episodes of intense deformation of Mesozoic and Tertiary age, and contrasts with the North Palawan block both in terms of stratigraphy and structural evolution. The rest of the archipelago is considered as the Philippine Mobile Belt. Approximately co-axial with the mobile belt is the Philippine Fault, a major strike slip fault that apparently developed partially in response to the kinematic forces from the subduction from the east and west of the mobile belt. Many areas of this mobile belt are underlain by ophiolitic complexes. Usually occurring together with pre-Cenozoic schists and phyllites, the ophiolitic rocks represent basement on which magmatic arcs have developed. The ages of the ophiolitic complexes range from Jurassic to early Paleogene. One of the best studied complete ophiolite sequence is the Zambales Ophiolite where tectonized peridotites progress to layered and isotropic gabbro, sheeted dike complex, pillow basalts and finally pelagic sedimentary rocks. Other ophiolitic complexes include those in Isabela, Polillo Island, eastern Rizal, Camarines Norte, Caramoan Peninsula, Mindoro, southern Palawan, Panay Island, Bohol Island, Leyte Island, Samar Island, Dinagat Island Group, north-central Zamboanga, Mindanao Central Cordillera and Pujada Peninsula. Ultramafic rocks of these ophiolites are hosts to significant deposits of chromite and nickel. Laterites over these rocks also contain economic deposits of secondary nickel minerals. On the other hand, massive sulphide and manganese deposits are associated with the volcanic and sedimentary carapace of the ophiolite. Ancient magmatic arcs in the mobile belt are characterized by thick volcanic flows intercalated with pyroclastic and sedimentary rocks and intrusions of diorite, quartz diorite and andesitic to dacitic rocks. Some intrusions, however, have a more alkalic character such as the syenites in Isabela and monzonites in Quirino and Nueva Vizcaya. The ages of the diorite intrusions vary, from late Early Cretaceous (Albian) in Cebu to Late Miocene-Pliocene (Black Mountain Quartz Diorite in Baguio District). Younger volcanic rocks, occurring as flows, intrusions and volcanic edifices disposed in linear belts are associated with active subduction processes. These are best exemplified by the Bataan volcanic belt and Bicol volcanic chain. Basement rocks Basement '''and '''crystalline basement are the rocks below a sedimentary platform or cover, or more generally any rock below sedimentary rocks or sedimentary basins that are metamorphic or igneous in origin. In the same way, the sediments or sedimentary rocks on top of the basement can be called a "cover" or "sedimentary cover". List of Basement rocks in the Philippines * Southern Cordillera Range ** Pugo Formation * Central Cordillera Range ** Lepanto Metavolcanics * Northern Cordillera ** Suyo Schist * Cagayan Valley Basin ** Abuan Formation * ''Central and Eastern ''Northern Sierra Madre ** Casiguran Ophiolite * Caraballo Range ** Caraballo Formation * Northern Sierra Madre ** Angat Ophiolite * Zambales Range ** Zambales Ophiolite * Southwest Luzon ** SanJuan Formation – Batangas ** Halcon Metamorphics – NE Mindoro ** Mansalay Formation – SW Mindoro ** Marinduque Formation – Marinduque ** Gumaca Schist – Bondoc * Southeast Luzon Basin ** Baleno Schist – Masbate Island ** Danao Schist – Ticao Island ** Makalawang Limestone – Burias and adjacent Islands * Southeast Luzon Arc ** Maliguit Formation – Quezon – Camarines Norte ** Siruma Schist – Caramoan Peninsula ** Yop Formation – Catanduanes ** Rapu-rapu Schist – Rapu-rapu Island ** Panganiran Peridotite – Bicol Peninsula * North Palawan Block ** Bacuit Formation – Northern Palawan **Romblon Metamorphic Complex – Romblon * South Palawan Block ** BeaufortUltramafic Complex – Southern Palawan * Panay Island ** Buruanga Metamophic Complex – Buruanga ** Antique Ophiolite – Antique ** Panpanan Formation – Central Panay-Iloilo Basin ** Sibala Formation – Eastern Panay * Negros ** Basak Formation * Cebu ** Tunlob Schist – Northern/Central Cebu ** Pandan Formation – Southern Cebu ** Kanglasog Volcanic Complex – Siquijor Island * Bohol ** Alicia Schist * Samar ** Samar Ophiolite * Leyte ** Malitbog Ophiolite – Western Leyte/Camotes Island ** Albuera Diorite – Central Highlands ** Tacloban Diorite – Eastern Leyte * Dinagat Group of Islands ** Nueva Estrella Schist * Sulu Archipelago ** Sulu Serpentinite * Zamboanga ** Tangauan Schist – Zamboanga Peninsula ** Dansalan Metamorphic Complex – North-Central Zamboanga ** Mangabel Formation – Sibuguey Peninsula * Central Mindanao ** Tago Schist * Agusan Davao Basin ** Adgaoan Formation – Agusan Basin ** Kabagtican Formation – Davao Basin ** Tagobo Conglomerate – Davao Gulf-Samal Island * Mindanao Pacific Cordillera ** Dinagat Ophiolite – Northern Pacific Cordillera ** Baggo Limestone – Central Pacific Cordillera ** Barcelona Formation – Southern Pacific Cordillera * Daguma Range ** Salbuyan Schist * Cotabato Basin ** Patut Formation * Sarangani Peninsula ** Malita Formation * Pujada Block ** Pujada Ophiolite Sedimentary basins Sedimentary basins located between arcs include the Ilocos-Central Valley Basin, Cagayan Valley Basin, southeast Luzon Basin, Visayan Sea Basin, Agusan-Davao Basin and Cotabato Basin. Ore deposits Gold and copper deposits in the Philippines tend to be clustered in certain areas such as Luzon Central Cordillera, Camarines Norte, Surigao and Davao, although large deposits may also be found elsewhere, as in Zambales (Dizon mine), Cebu (Atlas mine) and South Cotabato (Tampakan project). Many copper-gold deposits are associated with intrusions (mostly diorite and quartz diorite, but also monzonites and syenites) as well as Pliocene – Pleistocene volcanism (Lepanto mine at Mankayan, Benguet). Iron deposits are also associated with Neogene intrusions of diorite and quartz diorite.